This relates generally to electronic devices, and more particularly, to antennas for electronic devices with wireless communications circuitry.
Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry.
To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. At the same time, it may be desirable to support multiple communications bands to support a variety of desired services. Switches may be incorporated into devices for supporting the use of multiple antennas.
Switches and other components can exhibit non-linear behaviors. When radio-frequency signals are transmitted through these components, signal harmonics can be produced. These harmonics can cause interference for sensitive receivers.
To reduce the impact of harmonic interference, static low pass filters are sometimes coupled to the output of a switch. The low pass filters can help filter out aggressors such as harmonics that are produced by the non-linear behavior of a switch before these aggressors cause interference for victims such as sensitive wireless receivers in other communications bands. This type of low pass filter arrangement may, however, be of little or no use in many operating scenarios. For example, a low pass filter will not be able to protect circuitry such as a wireless local area network receiver at 2.4 GHz from interference at 2.4 GHz without disrupting cellular telephone traffic at frequencies above 2.4 GHz.